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# Peter W. Egolf - UNIVERSITY OF APPLIED SCIENCES OF WESTERN SWITZERLAND - REFRIGERAZIONE E RISCALDAMENTO MAGNETICO, EFFETTO PELTIER

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### Peter W. Egolf - UNIVERSITY OF APPLIED SCIENCES OF WESTERN SWITZERLAND - REFRIGERAZIONE E RISCALDAMENTO MAGNETICO, EFFETTO PELTIER

1. 1. High-frequency MagnetocaloricModules with Heat Gates Operatingwith Péltier EffectPeter W. EgolfUniversity of Applied Sciences of Western SwitzerlandInstitute of Thermal Sciences and EngineeringHEIG-VD / Hes-so
2. 2. In collaboration with:Institute of Micro and NanotechniquesLaurent GravierThibault FrancfortAnne-Gabrielle PawlowskiGilles CourretMirco Croci
3. 3. Table of content1) The operation principle of magneticrefrigeration2) The frequency problem3) The thermal switch technology4) Overall device: An engineer’s estimate5) Conclusions and outlook
4. 4. 1) The operation principle
5. 5. 2) The frequency problemA provocative personal statement:We are not competitive enough with present developments(feasibility was demonstrated, good efficiency is possible, butstill high cost)! Approaching luxury refrigerator sector!Demanded:3-5 x higher magnetocaloric effect of materialsor3-5 x higher frequency of the machines(seems to me more realistic!)
6. 6. 2) The frequency problem11010010001041050.01 0.1 1Frequencyf(Hz)Thickness of structure s (mm)Heat diffusion in andout of solid structure!Density:ρ=7900 kg m-3,Thermal conductivity:k=10.5 W m-1K-1,Heat capacity:cH= 886 J kg-1K-1,Thermal diffusivity:a= 1.5 10-6m2s-1.Example:s=0.25 mmf =100 Hzmax
7. 7. 2) The frequency problem0123450 0.2 0.4 0.6 0.8 1L=25 mmL=50 mmL=100 mmL=200 mmMaximalfrequencyf(Hz)Velocity v (m/s)Safety factor: 10L=25 mmL=50 mmL=100 mmL=200 mmSafety factor: 10Carry-over leakageExample:L=25 mmv=0.25 m/sResult:f ≤ 1 Hz
8. 8. 3) The thermal switch technologyAdvantage: Constant fluid flows with alternating cold/heatinputs (no carry over leckage, no fluid switches)MagneticfieldNofieldGate closedA. Kitanovski and P.W. Egolf, Int. J. Refr. 33 (3), 449-464:
9. 9. 3) The thermal switch technologyKitanovski and Egolf, Int. J. Refr. 33 (3), 449-464:The basic plates:
10. 10. 3) The thermal switch technologyThree main elements:1) Magnetocaloric layered bed2)Thermoelectric switches3) Micro channel heat exchangersOverall system and its performance132
11. 11. 3) The thermal switch technologyCharacteristic diameter of theNi wires is 200 nmSME: Dr. Anne-Gabrielle Paw-lowski, MNTNanowires:
12. 12. 3) The thermal switch technologyThermal switches and experimental device:
13. 13. 0204060801000 10 20Θ = 0Θ = 10Θ = 20Θ = 30Θ = 40Θ = 50COPΘ21111112112Θ+Θ−= CarnotCOPCOPEntire theory outlinedin Thermag V paper.Main result:( )chTRTTRIPP−==Θα2thTIIRPQα11 ==Θ( )ch TTAZ−ΘΘ=211Z: Figure of meritCoefficient of performance of a thermal switch:3) The thermal switch technology
14. 14. 4) Overall device: An engineer’s estimate  Thermal switches (3 layers):      20 Surface area of thermal switches A --- 800 cm221 Temperature difference Th-Tc --- 2 x 2.5 K22 Thermal resistance, Eq. (7d), Table 2 Rth --- ∞ +++23 Carnot coefficient of perf. (13a,b) COPCarnot --- 216…25424 Power thermoelectric effect, Eq. (3a) PT --- 10 mW25 Power electric loss, Eq. (3b) PR --- 122 mW26 Total power of source, Eq. (3c) PS --- 132 mW27 Heat flux, Eq. (10c) --- 0 +++28 First non-dim. variable, Eq. (11a,b) Q1 --- 0 +++29 Sec. non-dim. variable, Eq. (11c,d) Q2 --- 1230 Coeff. of perf.  (Eq.(13c)) COP --- 17-20 +++IQ
15. 15. 4) Overall device: An engineer’s estimateNo. Quantity Symbol ULMR(usual type)TSMR(thermal switch)   Overall machine:1 Nominal cooling power Pn 50 W* 50 W2 Max. cooling power Pmax 96 W 96 W3 Magnetic field strength (ind.) H 2 T* 2 T4 Frequency  f 2 Hz* 10 Hz5 Heat source temperature Tc -5 °C* -5 °C6 Heat sink temperature Th 45 °C* 45 °C7 Adiabatic temp. diff. ∆Tad5 K* 5 K8 Temp. Diff. Mat.-Fluid ∆T 1 K* 2.5 K9 Coeff. of perf. Carnot COPCarnot 5.4* 5.410 Coefficient of performance COP 2.8* 2.811 Exergy efficiency ξ 52 %* 52 %12 Number of layers (layered bed) N 10 1013 Specific cooling power pc 2.5 kW kg-1** 15 kW kg-1**14 Mass of magnetoc. mat.  mmagneto 384 g 64 g15 Volume of magnetoc. material V 49 cm38 cm316 Thickness of plates (FIG. 1) s ≈ 0.2 mm* 0.2 mm17 Surface area heat exchange A 4900 cm2400 cm218 Demanded heat transf. coeff. h 392 W m2K 1920 W m2K19 Estimate of magnets mass mmag 18 kg* 4-6 kg(*) Kitanovski et al. (2008a), (**) Kitanovski and Egolf (2008b) based on pure gadolinium.
16. 16. 5) Conclusions and outlook1) First nanowire thermal switches have been success-fully produced following secret recipes (patent)2) A substiantial Péltier effect was experimentally deter-mined3) The electric resistance can be further decreased4) The thermal resistance has not yet been successfullydetermined5) Thermal switches are high-frequency devices6) A physical model for the thermal switches has beendeveloped (see Thermag V proceedings)7) The energy demand of the switches is of small influence
17. 17. 5) Conclusions and outlook1)If this technology works, it will be possible to beatconventional refrigeration in numerous importantrefrigeration markets2)This technology is so promising that even automobilerefrigeration, where a high mass is very critical, couldbecome feasible!
18. 18. Final slideThank you for your attention!FINISH